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Edit File: TIFFRGBAImage.3tiff.html

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<h1 align=center>TIFFRGBAImage</h1>
<a href="#NAME">NAME</a> 
<a href="#SYNOPSIS">SYNOPSIS</a> 
<a href="#DESCRIPTION">DESCRIPTION</a> 
<a href="#ALTERNATE RASTER FORMATS">ALTERNATE RASTER FORMATS</a> 
<a href="#SIMULTANEOUS RASTER STORE AND DISPLAY">SIMULTANEOUS RASTER STORE AND DISPLAY</a> 
<a href="#SUPPORTING ADDITIONAL TIFF FORMATS">SUPPORTING ADDITIONAL TIFF FORMATS</a> 
<a href="#NOTES">NOTES</a> 
<a href="#RETURN VALUES">RETURN VALUES</a> 
<a href="#DIAGNOSTICS">DIAGNOSTICS</a> 
<a href="#SEE ALSO">SEE ALSO</a>

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<a name="NAME"></a>
<h2>NAME</h2>

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TIFFRGBAImageOK, TIFFRGBAImageBegin, TIFFRGBAImageGet,
TIFFRGBAImageEnd &minus; read and decode an image into a
raster
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<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>

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#include &lt;tiffio.h&gt;

typedef unsigned char TIFFRGBValue; typedef struct
_TIFFRGBAImage TIFFRGBAImage;

int TIFFRGBAImageOK(TIFF *tif, char
emsg[1024]) 
int TIFFRGBAImageBegin(TIFFRGBAImage *img,
TIFF* tif, int stopOnError,
char emsg[1024]) 
int TIFFRGBAImageGet(TIFFRGBAImage *img,
uint32* raster, uint32 width ,
uint32 height) 
void TIFFRGBAImageEnd(TIFFRGBAImage
*img)
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<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>

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The routines described here provide a high-level
interface through which TIFF images may be
read into memory. Images may be strip- or tile-based and
have a variety of different characteristics: bits/sample,
samples/pixel, photometric, etc. Decoding state is
encapsulated in a TIFFRGBAImage structure making it
possible to capture state for multiple images and quickly
switch between them. The target raster format can be
customized to a particular application&rsquo;s needs by
installing custom routines that manipulate image data
according to application requirements.

The default usage for these routines is: check if an
image can be processed using TIFFRGBAImageOK,
construct a decoder state block using
TIFFRGBAImageBegin, read and decode an image into a
target raster using TIFFRGBAImageGet, and then
release resources using TIFFRGBAImageEnd.
TIFFRGBAImageGet can be called multiple times to
decode an image using different state parameters. If
multiple images are to be displayed and there is not enough
space for each of the decoded rasters, multiple state blocks
can be managed and then calls can be made to
TIFFRGBAImageGet as needed to display an image.

The generated raster is assumed to be an array of
width times height 32-bit entries, where
width must be less than or equal to the width of the
image (height may be any non-zero size). If the
raster dimensions are smaller than the image, the image data
is cropped to the raster bounds. If the raster height is
greater than that of the image, then the image data are
placed in the lower part of the raster. (Note that the
raster is assume to be organized such that the pixel at
location (x,y) is
raster[y*width+x]; with the
raster origin in the lower-left hand corner.)

Raster pixels are 8-bit packed red, green, blue, alpha
samples. The macros TIFFGetR, TIFFGetG,
TIFFGetB, and TIFFGetA should be used to
access individual samples. Images without Associated Alpha
matting information have a constant Alpha of 1.0 (255).

TIFFRGBAImageGet converts non-8-bit images by
scaling sample values. Palette, grayscale, bilevel,
CMYK , and YCbCr images are converted to
RGB transparently. Raster pixels are returned
uncorrected by any colorimetry information present in the
directory.

The parameter stopOnError specifies how to act if
an error is encountered while reading the image. If
stopOnError is non-zero, then an error will terminate
the operation; otherwise TIFFRGBAImageGet will
continue processing data until all the possible data in the
image have been requested.
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<a name="ALTERNATE RASTER FORMATS"></a>
<h2>ALTERNATE RASTER FORMATS</h2>

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To use the core support for reading and processing
TIFF images, but write the resulting raster
data in a different format one need only override the
&lsquo;&lsquo;put methods&rsquo;&rsquo; used to store
raster data. These methods are are defined in the
TIFFRGBAImage structure and initially setup by
TIFFRGBAImageBegin to point to routines that pack
raster data in the default ABGR pixel format.
Two different routines are used according to the physical
organization of the image data in the file:
PlanarConfiguration=1 (packed samples), and
PlanarConfiguration=2 (separated samples). Note that
this mechanism can be used to transform the data before
storing it in the raster. For example one can convert data
to colormap indices for display on a colormap display.
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<a name="SIMULTANEOUS RASTER STORE AND DISPLAY"></a>
<h2>SIMULTANEOUS RASTER STORE AND DISPLAY</h2>

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It is simple to display an image as it is being read into
memory by overriding the put methods as described above for
supporting alternate raster formats. Simply keep a reference
to the default put methods setup by
TIFFRGBAImageBegin and then invoke them before or
after each display operation. For example, the
tiffgt(1) utility uses the following put method to
update the display as the raster is being filled:

<pre>static void
putContigAndDraw(TIFFRGBAImage* img, uint32* raster,
 uint32 x, uint32 y, uint32 w, uint32 h,
 int32 fromskew, int32 toskew,
 unsigned char* cp)
{
 (*putContig)(img, raster, x, y, w, h, fromskew, toskew, cp);
 if (x+w == width) {
 w = width;
 if (img-&gt;orientation == ORIENTATION_TOPLEFT)
 lrectwrite(0, y-(h-1), w-1, y, raster-x-(h-1)*w);
 else
 lrectwrite(0, y, w-1, y+h-1, raster);
 }
}
</pre>

(the original routine provided by the library is saved in
the variable putContig.)
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<a name="SUPPORTING ADDITIONAL TIFF FORMATS"></a>
<h2>SUPPORTING ADDITIONAL TIFF FORMATS</h2>

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The TIFFRGBAImage routines support the most
commonly encountered flavors of TIFF. It is
possible to extend this support by overriding the
&lsquo;&lsquo;get method&rsquo;&rsquo; invoked by
TIFFRGBAImageGet to read TIFF image
data. Details of doing this are a bit involved, it is best
to make a copy of an existing get method and modify it to
suit the needs of an application.
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<a name="NOTES"></a>
<h2>NOTES</h2>

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Samples must be either 1, 2, 4, 8, or 16 bits.
Colorimetric samples/pixel must be either 1, 3, or 4 (i.e.
SamplesPerPixel minus ExtraSamples).

Palette image colormaps that appear to be incorrectly
written as 8-bit values are automatically scaled to
16-bits.
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<a name="RETURN VALUES"></a>
<h2>RETURN VALUES</h2>

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All routines return 1 if the operation was successful.
Otherwise, 0 is returned if an error was encountered and
stopOnError is zero.
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<a name="DIAGNOSTICS"></a>
<h2>DIAGNOSTICS</h2>

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All error messages are directed to the
TIFFError(3TIFF) routine.

Sorry, can not handle %d-bit pictures. The image
had BitsPerSample other than 1, 2, 4, 8, or 16.

Sorry, can not handle %d-channel images. The image
had SamplesPerPixel other than 1, 3, or 4.

Missing needed &quot;PhotometricInterpretation&quot;
tag. The image did not have a tag that describes how to
display the data.

No &quot;PhotometricInterpretation&quot; tag, assuming
RGB. The image was missing a tag that describes how to
display it, but because it has 3 or 4 samples/pixel, it is
assumed to be RGB.

No &quot;PhotometricInterpretation&quot; tag, assuming
min-is-black. The image was missing a tag that describes
how to display it, but because it has 1 sample/pixel, it is
assumed to be a grayscale or bilevel image.

No space for photometric conversion table. There
was insufficient memory for a table used to convert image
samples to 8-bit RGB.

Missing required &quot;Colormap&quot; tag. A
Palette image did not have a required Colormap
tag.

No space for tile buffer. There was insufficient
memory to allocate an i/o buffer.

No space for strip buffer. There was insufficient
memory to allocate an i/o buffer.

Can not handle format. The image has a format
(combination of BitsPerSample,
SamplesPerPixel, and
PhotometricInterpretation) that can not be
handled.

No space for B&amp;W mapping table. There was
insufficient memory to allocate a table used to map
grayscale data to RGB.

No space for Palette mapping table. There was
insufficient memory to allocate a table used to map data to
8-bit RGB.
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<a name="SEE ALSO"></a>
<h2>SEE ALSO</h2>

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TIFFOpen(3TIFF), TIFFReadRGBAImage(3TIFF),
TIFFReadRGBAImageOriented(3TIFF),
TIFFReadRGBAStrip(3TIFF),
TIFFReadRGBATile(3TIFF), libtiff(3TIFF)

Libtiff library home page:
http://www.remotesensing.org/libtiff/
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